Controlled lactide polymerization using diimine magnesium complex: synthesis of high-molecular-weight polylactide and evaluation of its cytotoxicity in vitro

A mechanism of ring-opening polymerization of lactide in a solution using a magnesium coordination compound (dpp-bian)Mg(thf)(3) (1) containing a chelating redox-active acenaphthenediimine ligand dpp-bian (1,2-bis-[(2,6- diisopropyl)phenylimino]acenaphthene) has been proposed. The reaction proceeds in the presence of a chain initiator/regulator ROH (R = H, alkyl, acyl), while the true polymerization catalyst is presumably the product of the interaction of complex 1, lactide, and ROH. It has been demonstrated that a decrease in the content of the initiating impurity in the initial monomer by precise purification of the latter makes it possible to control the molecular weight of polymer in order to obtain high molecular weight polylactide (M-w = 1.9 center dot 10(5), PDI 1.5). Due to non-toxic catalyst system, the resulting polymer shows no cytotoxicity, as confirmed by in vitro studies.